The present invention relates to a specific gravity detector using an electromechanical vibrator which comprises piezoelectric ceramic members, for example, and vibrates about its central axis, and has a detector member which is immersed in liquid to measure the specific gravity thereof and which is vibrated via the electromechanical vibrator about its central axis, which central axis is coaxial with the central axis of the electromechanical vibrator, to measure the specific gravity of the liquid based on a variation in the resonance frequency of the vibrator corresponding to the moment of inertial of the liquid.
Float-type and tuning fork-type specific gravity detectors are typical ones which have heretofore been proposed in the art. The float-type specific gravity detector detects the amount of rise and fall of a float member within liquid to measure the specific gravity of the liquid. The tuning fork-type specific gravity detector detects the variation in the resonance frequency of its forks filled with liquid to be measured to measure the specific gravity of the liquid.
The float-type specific gravity detector has limited utility due to the facts that the float member has to be horizontally placed in position and a large volume of sample liquid must be prepared. It further has disadvantages in that is is mechanically complex and is likely to have to be large in size and in that high precision measurement cannot be expected.
The tuning fork-type specific gravity detector is required to have its U-shaped forks filled with sample liquid and, if the amount of the liquid in the forks is insufficient, the accuracy of the measurement is unsatisfactory. Further, since sound waves are propagated within the liquid contained in the container in which the forks are immersed, and are reflected by the inner walls of the container, an error in measurement will be made depending on the size of the container.
The present inventors conducted studies on a specific gravity detector capable of eliminating the aforementioned disadvantages and conceived a method of measuring the specific gravity of liquid by using an electromechanical vibrator, connecting the vibrator to a detector member, immersing the detector member within the liquid, transmitting the mechanical vibration of the vibrator to the detector member, and converting a variation in the resonance frequency of the vibrator corresponding to the moment of inertia of the liquid into equivalent electric vibration. In accordance with their idea, they tried to use a commercially available vibrator vibrating in the direction of its thickness as the electromechanical vibrator. As a result, it was found that the vibrator connected to a detector member caused the detector member to be vibrated vertically relative to the surface of the liquid, thereby producing vibration waves propagating within the liquid and thus making it difficult to measure the specific gravity of the liquid with a high degree of precision.